Since becoming interested in the history of cryptography, I've become obsessed with the Vounich Manuscript (VMS), a currently-unreadable manuscript that appears to date from the 15th or 16th century. There are a couple of sources in the bibliography for this page. My own analyses and thoughts will be put online sporadically.

Medieval Cryptography

This is the outline/handout for a class I first taught at Pennsic in 2004. Most of the
information here is derived from Kahn 1996 (see references).

For the particularly geeky, I wrote a set of functions for the statistical package
R to decode or encode ciphers with a
key letter, with a word as a key, or as an autokey.
There are examples of all these types of cipher below.

If you are curious, but don't have or use R, no worries. First, find an Rweb server like this one. Then, copy the contents of the appropriate file above and paste them into the Rweb window. Finally, type in the correct command for what you want to do. Press the submit button, and after a bit your answer will be at the bottom of the page, after a bunch of R code.

Here are some hints, along with an example for each of the three functions.

key letter - either the plaintext or the ciphertext, plus the keyletter
letterkey(plain="plaintext in quotes", keyletter="Q")
or
letterkey(cipher="ciphertext in quotes", keyletter="Q")
letterkey(plain="the east and midrealm are at war", keyletter="B")

key word - either the plaintext or the ciphertext, plus the key word (or phrase)
wordkey(plain="plaintext in quotes", keyword="WORD")
or
wordkey(cipher="ciphertext in quotes", keyword="WORD")
wordkey(plain="the east and midrealm are at war", keyword="ABCDEFGHIJKLMNOPQRSTUVWXYZ")
wordkey(plain="the east and midrealm are at war", keyword="PENNSIC WAR")

autokey - either the plaintext or the ciphertext, plus the initial key letter
autokey(plain="plaintext in quotes", keyletter="Q")
or
autokey(cipher="ciphertext in quotes", keyletter="Q")
autokey(plain="the east and midrealm are at war", keyletter="F")

Basic terminology

steganography - hide the existence of the message

cryptography - make the message hard to read

transposition - rearrange the letters

substitution - use something different instead

code - substitute by word or idea

cipher - substitute by letter

monoalphabetic - one letter = one symbol

polyalphabetic - one letter = several possible symbols

homophonic - some letters have several equivalents

nomenclator - mix of code and cipher

The earliest beginnings

Egypt - showoff scribes

India - highly developed, along with grammar and linguistics; mentioned in Kama Sutra

Hebrew - three kinds of monoalphabetic ciphers appear in the Old Testament

Classical - On the Defense of Fortified Places by Aeneas Tacticus is the first surviving written material, describes military uses of cryptography (4th c. BCE)
includes steganography with string - punch holes in a disk for the letters, thread string thru to spell out the message

Polybius square - developed for signalling by Greek historian Polybius, but still used in cryptography (2nd c. BCE)

1

2

3

4

5

1

A

B

C

D

E

A = 11

2

F

G

H

I/J

K

B = 12

3

L

M

N

O

P

M = 32

4

Q

R

S

T

U

Z = 55

5

V

W

X

Y

Z

...

Julius Caesar - first claim of actual military use (1st c. BCE)
alphabet offset by some number is still called a Caesar alphabet

Plaintext

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

Cipher

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

Medieval examples

Arab world - highly developed, including first text on cryptanalysis using letter frequencies
doesn't seem to have influenced Western world

Cryptography used to conceal information, especially magic / alchemy
Often used symbols instead of letters

Viking crytography - monoalphabetic substitution ciphers on the Rök runestone, Gotland, Sweden
Runic cryptography was based on the group and place of each rune. The elder futhark had 24 runes in 3 groups, so one part of the symbol used indicated which of the three groups, and the other part which of the eight possible places that rune occupied.

Irish ogham - wide variety of encryptions described by the Book of Ballymote (15th c.)
"serpent through the heather", "great speckle", "vexation of a poet's heart"

Hildegard von Bingen - cipher alphabet given to her in a flash of inspiration (11th c.)

Roger Bacon - wrote about cryptography in Secret Works of Art and the Nobility of Magic (13th c.)
"A man is crazy who writes a secret in any other way than one which will conceal it from the vulgar."

Geoffrey Chaucer (maybe) - monoalphabetic substitution cipher to conceal important information within The Equatorie of the Planetis

Renaissance achievements

Cryptography widely used for diplomatic purposes, especially among the Italian city-states
full-time cipher secretaries for making and breaking codes and ciphers
used nulls, concealed word length, other ways of making things more difficult

nomenclators used from 15th - 19th centuries
code words for common/important terms, cipher for the rest

Leon Batista Alberti - first European publication on frequency analysis (15th c.)
developed the idea of using multiple cipher alphabets (switching every few words)
developed the cipher disk

Kahn, David. 1996. The Codebreakers: the Story of Secret Writing. Second edition. Scribener, NY.
best book on the history of cryptography, and source of most of the material here
very large, and mostly about World War II